1. Field
The present application relates generally to optical gyroscopes, and more specifically, to optical gyroscopes utilizing a laser source.
2. Description of the Related Art
First demonstrated in the 1970s, the fiber-optic gyroscope (FOG) is one of the oldest and most advanced fiber optic sensors. It has found many commercial and military applications. Part of this success is rooted in the Sagnac loop that it uses as the sensing element, a common-path interferometer that is inherently reciprocal and thus highly stable against most external perturbations. Another component of this success is the use of broadband light, for example from an Er-doped superfluorescent fiber source (SFS), to interrogate the interferometer. Incoherent light was shown very early on to essentially eliminate two deleterious effects that occur in the fiber loop, namely a non-reciprocal phase drift induced by the nonlinear Kerr effect and noise and long-term phase drift caused by coherent backscattering. See, e.g., H. C. Lefevre, The Fiber-Optic Gyroscope, Artech House, Boston (1993).
Unfortunately, the adoption of a broadband source introduced two limitations. First, the noise of a broadband source (excess noise) typically far exceeds shot noise, and it limits the FOG's minimum detectable rotation rate. Second, the scale factor of a FOG, which relates the measured gyroscope signal to the rotation rate, must be extremely stable (˜1 part per million) for aircraft inertial navigation applications. Consequently, the mean wavelength of the light must have a comparable stability, which is difficult to achieve in practice with a broadband source.